In general, nitride of a group III element, such as gallium nitride (GaN), having excellent thermal stability and a direct-transition type energy band structure, has recently come to prominence as a material for a light emitting element in a visible ray and ultraviolet region. In particular, blue and green light emitting elements using indium gallium nitride (InGaN) are utilized in various applications such as a large-scale full color flat panel display device, a traffic light, interior illumination, a high density light source, a high resolution output system, optical communication, and the like.
Since it is difficult to fabricate a homogenous substrate for growing a semiconductor layer made of nitride of a group III element, the semiconductor layer made of nitride of a group III element is generally grown on a heterogeneous substrate having a similar crystal structure through metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or the like. As the heterogeneous substrate, a sapphire substrate having a hexagonal structure is commonly used.
However, an epitaxial layer grown on the heterogeneous substrate has a relatively high dislocation density due to a lattice mismatch and a difference in thermal expansion coefficients with the growth substrate. The epitaxial layer grown on the sapphire substrate is known to generally have a dislocation density of 1E8/cm2 or more. Thus, there is a limitation in improving luminous efficiency of a light emitting diode (LED) by the epitaxial layer having such a high dislocation density.
In addition, when the LED is operated with a high current, since the current is concentrated through dislocation, luminous efficiency is further reduced in comparison to an operation of the LED with a low current.